Whitaker has come under scrutiny since his appointment for opinion pieces he wrote for The Hill and CNN advocating for curbing the scope of the Mueller investigation, and suggesting stifling its funding. He penned both pieces prior to joining the Department of Justice as chief of staff to Sessions.

Skeptics of any such effort by Whitaker to cut funding have noted that Mueller's budget for fiscal year 2019 has already been approved.

Rep. Jerrold Nadler (D-N.Y.), likely the incoming chairman of the House Judiciary Committee, signaled on Sunday he would call on Whitaker to appear before lawmakers to answer questions about his appointment.

“Our very first witness on — after Jan. 3 — we will subpoena ... or we will summon — if necessary, subpoena, Mr. Whitaker,” Nadler said on CNN’s “State of the Union.”